Numerous clinical reports describe the recurrence of solid tumors and leukemias in patients years after successful treatment of the primary neoplasm. These reports suggest that small numbers of tumor cells persist in a dormant state in patients during periods of prolonged clinical remission. The objectives of this research are to determine whether endogenous viruses and the immune responses to them play an important role in the establishment and maintenance of the tumor dormant state established in DBA/2 mice with L5178Y lymphoma cells. We will determine in vitro whether immune responses to endogenous viruses are present in tumor dormant mice, and identify the viral antigens to which they are directed. We will then determine whether these immune responses function in vivo to maintain the L5178Y cell tumor dormant state, and finally attempt to prolong the tumor dormant state by stimulating immune responses to virus antigens on the surface of L5178Y cells.